1. Field of the Invention
The present invention relates to a control system for an electronic apparatus such as an information processing unit, an input unit for inputting data into this electronic apparatus and a key for use in this input unit.
2. Description of the Related Art
Keyboards are conventionally used as data input units for entering data into information processing units (hereinafter referred to as IPUs).
In general, such a keyboard is connected to an IPU through a cable or the like. A plurality of keys are provided on the keyboard. The respective keys work as electric switches. When a user depresses a key, a predetermined signal for identifying that key is generated. This signal is transmitted to the IPU through the cable.
Since the conventional keyboard is connected to the IPU through the cable, it has the disadvantage that the distance between the IPU and the keyboard is bound by the length of the cable, that is the keyboard cannot be located at a longer distance from the IPU than the length of the cable, reducing the usability of the keyboard.
In view of the above disadvantage, a prior art system for dispensing with any such cable for connecting a keyboard to an IPU by acoustically connecting the keyboard to the IPU is disclosed in Japanese Patent Application Laid-Open No. Sho 58-132834. This prior art system is shown in FIG. 10.
Referring to FIG. 10, a keyboard 80 has a plurality of keys (not shown), keyboard circuit 81 for producing a digital signal corresponding to the depressed key when each of the keys is depressed, a converter 82 for converting this digital signal into a signal of a unique frequency, an amplifier 83 for amplifying the signal converted by the converter 82, a speaker 84 driven by the signal amplified by the amplifier 83 to generate an acoustic signal (i.e., a sound), and a battery 85 for transmitting an electrical power to these components.
An IPU 90 has a microphone 91 for receiving the acoustic signal generated by the speaker 84 and sending this acoustic signal to an amplifier 92, which then amplifies the acoustic signal, a converter 93 for converting the acoustic signal amplified by the amplifier 92 into a digital signal on the basis oh the frequency of the amplified acoustic signal, a control circuit 94 for controlling the IPU 90, a display unit 95 for displaying data, a power supply controller 96 for supplying electrical power to the IPU 90 and a power supply line 97 connecting the controller 96 to the commercial power supply source (not shown).
As described above, according to this prior art system, the keyboard and the IPU are acoustically connected to each other to thereby dispense with any cables for connecting the keyboard to the IPU.
However, in the prior art system, the keyboard 80 must be supplied with electrical power by the battery 85. Where the electrical charge stored in the battery 85 has run out, the system has the disadvantage that it is necessary for the user to perform a troublesome operation of replacing the battery 85 for a new one, or recharging the battery 85 if it is rechargeable battery.